Kasuga grows up at an orphanage. Even though five people send money and letters to him until he leaves the orphanage at the age of 15, he doesn't know who they are and why they supported him. He looks for them. He meets Natsumi, who is one of them. Kasuga meets Yasuhiro, who is also a 15-year-old boy, at Natsumi's place. Natsumi used to be Yasuhiro's mother's husband. Yasuhiro is in love with Natsumi and wants to live with him. Natsumi, Yasuhiro and Kasuga end up living together.